A variety of regulatory molecules, known as cytokines, have been identified including interleukin- 11 (IL-11). IL-11 stimulates a variety of hematopoietic and immune functions. The various protein forms of IL-11 and DNA encoding various forms of IL-11 activity are described in Bennett, et al., U.S. Pat. No. 5,215,895 (June 1, 1993); McCoy, et al., U.S. Pat. No. 5,270,181 (Dec. 14, 1993); and McCoy, et al., U.S. Pat. No. 5,292,646 (Mar. 8, 1994), and incorporated herein by reference. Thus, the term "IL-11" includes protein produced by recombinant genetic engineering techniques; purified from cell sources producing the factor naturally or upon induction with other factors; or synthesized by chemical techniques; or a combination of the foregoing.
To maximize the pharmacological benefit of any protein, it is essential to have finished dosage forms that are stable, easily and reproducibly manufactured, and designed for standard routes of administration. Specifically, it is desirable to have stable, concentrated forms of bulk protein, e.g., IL-11 which, in turn, are suitable for further manufacture of finished dosage forms of protein, which can then be administered e.g., via sub cutaneous injection.
In both bulk protein and finished dosage forms, protein stability can be affected by such factors as ionic strength, pH, temperature, repeated cycles of freeze/thaw and shear forces. Active protein may be lost as a result of physical instabilities, including denaturation and aggregation (both soluble and insoluble aggregate formation), as well as chemical instabilities, including, for example, hydrolysis, deamidation, and oxidation, to name just a few. For a general review of stability of protein pharmaceuticals, see, for example, Manning, et al., Pharmaceutical Research 6:903-918 (1989). In addition, it is desirable to maintain stability in the absence of carrier proteins.
While it is widely appreciated that these possible protein instabilities can occur, until a protein has been studied it is impossible to predict the particular instability problems that a particular protein may have. Any of these instabilities can potentially result in the formation of a protein or protein by-product or derivative having lowered activity, increased toxicity, and/or increased immunogenicity. Indeed, protein precipitation can lead to thrombosis, non-homogeneity of dosage form and immune reactions. Thus, the safety and efficacy of any pharmaceutical formulation of a protein is directly related to its stability.
Accordingly, there continues to exist a need in the art for methods for improving protein stability during the concentration process as well as providing stability in the absence of other carrier proteins in a concentration sufficiently high for various routes of administration including, e.g., sub cutaneous injection, intra venous injection.